System and Method for Temperature Based Control of a Power Semiconductor Circuit

ABSTRACT

In a method for operating a power semiconductor circuit a power semiconductor chip is provided which includes a power semiconductor switch with a first load terminal and with a second load terminal. Further, a first temperature sensor which is thermally coupled to the power semiconductor switch and a second temperature sensor are provided. The power semiconductor switch is switched OFF or kept switched OFF if the temperature difference between a first temperature of the first temperature sensor and a second temperature of the second temperature sensor is greater than or equal to a switching-OFF threshold temperature difference which depends, following an inconstant first function, on the voltage drop across the power semiconductor switch between the first load terminal and the second load terminal.

This application is a continuation of U.S. application Ser. No.12/242,266 entitled, “System and Method for Temperature Based Control ofa Power Semiconductor Circuit” which was filed on Sep. 30, 2008 and isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The invention relates to power semiconductor circuits.

BACKGROUND

Power semiconductor circuits are used, inter alia, to provide electricalloads with electrical power. For this purpose, the power semiconductorcircuit comprises at least one controllable power semiconductor switch.As such a power semiconductor switch produces waste heat, there is adanger of overheating the power semiconductor switch. Hence, there is aneed for an effective protection concept.

SUMMARY OF THE INVENTION

A method for operating a power semiconductor circuit arrangement isprovided. In the method, a power semiconductor chip is provided whichcomprises a power semiconductor switch with a first load terminal andwith a second load terminal. Then, a first temperature sensor which isthermally coupled to the power semiconductor switch and a secondtemperature sensor are provided. The power semiconductor switch isswitched OFF or kept switch switched OFF if the temperature differencebetween a first temperature of the first temperature sensor and a secondtemperature of the second temperature sensor is greater than or equal toa switching-OFF threshold temperature difference which depends,following an inconstant first function, on the voltage drop across thepower semiconductor switch between the first load terminal and thesecond load terminal.

Further, a power semiconductor circuit arrangement is provided. Thepower semiconductor circuit arrangement includes a power semiconductorchip, a first temperature sensor, and a second temperature sensor. Thepower semiconductor chip comprises a power semiconductor switch with afirst load terminal and with a second load terminal. The firsttemperature sensor is thermally coupled to the power semiconductorswitch. The power semiconductor circuit arrangement further comprises anelectrical circuit which is designed to switch OFF the powersemiconductor switch or to keep the power semiconductor switch switchedOFF if the temperature difference between a first temperature of thefirst temperature sensor and a second temperature of the secondtemperature sensor is greater than or equal to a switching-OFF thresholdtemperature difference which depends, following an inconstant firstfunction, on the voltage drop across the power semiconductor switchbetween the first load terminal and the second load terminal.

Then, a power semiconductor circuit arrangement is provided. The powersemiconductor circuit arrangement includes a power semiconductor chip, afirst temperature sensor, and a second temperature sensor. The powersemiconductor chip comprises a power semiconductor switch with a firstload terminal, a second load terminal, and a control input terminal. Thefirst temperature sensor is thermally coupled to the power semiconductorswitch. The arrangement further includes a temperature differenceevaluation unit, a threshold providing unit, and a comparator unit. Thetemperature difference evaluation unit is designed to provide a firstvoltage at a first output, the first voltage representing thetemperature difference between the temperature of the first temperaturesensor and the temperature of the second temperature sensor. Thethreshold providing unit is designed to provide a second voltage at asecond output, the second voltage representing a switching-OFF thresholdtemperature difference from an inconstant first function at a voltagedifference measured between the first load terminal and the second loadterminal, wherein the first function is a switching-OFF thresholdtemperature difference depending on a voltage drop. The comparator unitcomprises a first comparator input, a second comparator input, and acomparator output, wherein the first output is electrically connected tothe first comparator input, wherein the second output is electricallyconnected to the second comparator input, and wherein the comparatoroutput is electrically connected to the control input of the powersemiconductor switch. The comparator unit is designed to provide asignal causing the power semiconductor switch to remain or to beswitched in the OFF-state, if the voltage difference between the firstvoltage and the second voltage implies that a temperature differencedetermined by the temperature difference evaluation unit is greater thanor equal to a switching-OFF threshold temperature difference determinedby the first threshold providing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of examples and are incorporated in and constitute a partof this specification. The drawings illustrate examples of the inventionand together with the description serve to explain principles of theinvention. Other examples and many of the intended advantages ofexamples will be readily appreciated as they become better understood byreference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 is a simplified circuit diagram of a power semiconductor circuitarrangement;

FIG. 2A is a simplified circuit diagram explaining a possible embodimentof a first threshold providing unit as used in the power semiconductorcircuit arrangement of FIG. 1;

FIG. 2B is a simplified circuit diagram explaining a possible embodimentof a second threshold providing unit as used in the power semiconductorcircuit arrangement of FIG. 1;

FIG. 3A is a diagram showing possible shapes of a switching-OFFthreshold temperature difference curve and of two different switching-ONthreshold temperature difference curves;

FIG. 3B is a diagram showing some cycles of a curve of the temperaturedifference between the first temperature and the second temperature, asa function of the voltage difference between the first load terminal andthe second load terminal of the power semiconductor switch whenswitching ON a load;

FIG. 4 is a diagram showing the electrical current through the powersemiconductor switch, and the temperature difference between the firsttemperature and the second temperature, as a function of the time t,when switching ON the power semiconductor switch;

FIG. 5 is a diagram showing the electrical current through the powersemiconductor switch, and the temperature difference between the firsttemperature and the second temperature, as a function of the time t, inthe case of an electric short circuit; and

FIG. 6 is top view of power semiconductor chip comprising all componentsshown in FIG. 1, except the load and the power supply V_(B).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific examples in which the invention may bepracticed. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of examples can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother examples may be utilized and structural or logical changes may bemade without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryexamples described herein may be combined with each other, unlessspecifically noted otherwise.

FIG. 1 is a simplified circuit diagram of a power semiconductor circuitarrangement 100. The arrangement 100 comprises a power semiconductorswitch 1 with a first load terminal 11, a second load terminal 12, and acontrol input 13. The power semiconductor switch 1 may be anycontrollable power semiconductor switch, e.g., a MOSFET, DMOStransistor, a VMOS transistor, an IGBT, a JFET, a bipolar transistor, athyristor, e.g., a GTO (GTO=gate turn off thyristor), etc. Depending onthe selected type of the controllable power semiconductor switch 1, thepair of load terminals 11/12 may be drain/source or source/drain oremitter/collector or collector/emitter or anode/cathode orcathode/anode. The control input 13 may be a gate electrode or a baseelectrode, or, in case of a light triggered power semiconductor switch,an optically sensitive area of the switch.

In the present example, the power semiconductor switch 1 is a DMOStransistor. An arbitrary electrical load 7, for example, an incandescentlamp, a motor, etc. is connected in series with the power semiconductorswitch 1 and connected to the second load terminal 12. Alternatively,the electrical load 7 could also be connected to the first load terminal11.

In order to provide electrical energy to the load 7, a power supplyvoltage V_(B) is applied to the series connection of the powersemiconductor switch 1 and the load 7. For example, the supply voltageV_(B) may be a battery voltage in automotive applications, or a DC-linkvoltage (DC-link=direct current link) in power conversion applications.

In the ON-state of the power semiconductor switch 1, an electric currentI_(DS) flows through the power semiconductor switch 1 and the load 7.Otherwise, in the OFF-state of the power semiconductor switch 1, apartfrom an insignificant leakage current, there is no current flowingthrough the power semiconductor switch 1.

Further, a gate driving unit 5 is provided so as to control the powersemiconductor switch 1, i.e., the gate driving unit 5 is designed toswitch the power semiconductor switch 1 from the ON-state to theOFF-state, or vice versa. To this, the gate driving unit 5 comprises anoutput 53 which is electrically connected to the control input 13 of thepower semiconductor switch 1.

If the power semiconductor switch 1 is switched ON, the temperature T1of the power semiconductor switch 1 which is referred to as “firsttemperature” will increase due to the power loss of the switch 1. Thetemperature T1 depends in particular on the current I_(DS) through thepower semiconductor switch 1, on the power-ON time of the powersemiconductor switch 1, and on the resistance of the power semiconductorswitch 1 in the ON-state (R_(ON)).

In order to avoid overheating the power semiconductor switch 1, a firsttemperature sensor 21, which is thermally coupled to the powersemiconductor switch 1, is provided. In FIG. 1, the thermal coupling issymbolized by a dashed line 15 between the power semiconductor switch 1and the first temperature sensor 21. For example, the first temperaturesensor 21 may be integrated in the power semiconductor chip close to thepower semiconductor switch 1.

Then, a second temperature sensor 22 is arranged distant from the firsttemperature sensor 21. For example, the second temperature sensor 22 mayalso be integrated in the same power semiconductor chip as the powersemiconductor switch 1, but distant therefrom so as to measure atemperature different from the temperature of the power semiconductorswitch 1. Alternatively, it is possible to arrange the secondtemperature sensor 22 at a location outside the semiconductor chip. Inthe sense of any of the above described possibilities, the secondtemperature sensor 22 is regarded to be thermally decoupled from thepower semiconductor chip 1, and therefore will have a second temperatureT2 which is different from the first temperature T1. In manyapplications addressed by the present invention, the first temperatureT1 will, at least temporarily, be higher than or equal to the secondtemperature T2, i.e. a temperature difference ΔT=T1−T2 will be greaterthan or equal to zero.

In FIG. 1, a temperature difference evaluation unit 8 determines thetemperature difference ΔT=T1−T2. In this sense, “determine” may, butdoes not necessarily mean, that the temperature difference evaluationunit 8 provides a temperature difference ΔT which may be expressed inunits like “K” (Kelvin), “° C.” (degrees centigrade) or “° F.” (degreesFahrenheit). Generally, it is sufficient if the temperature differenceevaluation unit 8 provides a first signal which is a measure for thetemperature difference ΔT. For example, the first signal may be anelectric current, or, as exemplary shown in FIG. 1, an electric voltageV1 representing a difference between signals 81 and 82 from temperaturesensors 22 and 21, respectively. In other words, the provided firstsignal is a function f(ΔT) depending on the temperature difference ΔT.

In FIG. 1, the first signal is provided at an output 83 of thetemperature difference evaluation unit 8 and fed to a first input 31 ofa first comparator unit 3. The first comparator unit 3 further comprisesa second input 32 which is electrically connected to an output 93 of afirst threshold providing unit 9 in order to receive a second signalgenerated by the first threshold providing unit 9. The second signal maybe, for example, an electric current, or, as exemplary shown in FIG. 1,an electric voltage V2. The second signal is an inconstant functionf2(V_(DS)) of the voltage drop V_(DS) across the power semiconductorchip 1, i.e., of the voltage V_(DS) between the first load terminal 11and the second load terminal 12, and represents a predefinedswitching-OFF threshold temperature difference ΔT_(OFF) in order toprovide for switching OFF the power semiconductor chip 1 or to keep thepower semiconductor chip 1 in the OFF-state, if the temperaturedifference ΔT=T1−T2 is greater than or equal to the thresholdtemperature difference ΔT_(OFF).

FIG. 3A shows a possible shape of a switching-OFF threshold temperaturedifference curve ΔT_(OFF), and of two possible switching-ON thresholdtemperature difference curves ΔT_(ON)(1) and ΔT_(ON)(2), each curvedepending on the voltage drop V_(DS) across the power semiconductor chip1 as described above with reference to FIG. 1. As shown in the exampleof FIG. 3A, the switching-OFF threshold temperature difference curveΔT_(OFF) is inconstant and may comprise, e.g., an optional constantsection (in the example in a range from V_(DS)=0 V to 4 V), an optionallinear falling section (in the example in a range from V_(DS)=4 V to 16V), and an optional constant section (in the example in a range aboveV_(DS)=16 V). In other examples, the switching-OFF threshold temperaturedifference curve ΔT_(OFF) may also be curved.

The switching-ON threshold temperature difference curve ΔT_(ON)(2) doesnot exceed the switching-OFF threshold temperature difference curveΔT_(OFF). The switching-ON threshold temperature difference curveΔT_(ON)(2) may, e.g., also have an optional constant section (in theexample in a range from V_(DS)=0 V to 4 V), an optional linear fallingsection (in the example in a range from V_(DS)=4 V to 16 V), and anoptional constant section (in the example in a range above V_(DS)=16 V).In the example of FIG. 3A, the difference between the switching-OFFthreshold temperature difference curve ΔT_(OFF) and the switching-ONthreshold temperature difference curve ΔT_(ON)(2) is constant over thewhole range of V_(DS). In the example, the difference is about 20 K.

An other example for a possible switching-ON threshold temperaturedifference curve is curve ΔT_(ON)(1) which is constant over the wholerange of V_(DS).

In the following FIG. 3B, the mode of operation of the arrangement 100shown in FIG. 1 will be explained, by way of example, for theswitching-OFF threshold temperature difference curve ΔT_(OFF) and theswitching-ON threshold temperature difference curve ΔT_(ON)(2) asexplained with reference to FIG. 3A, in combination with a load 7, theresistance of which increases after being supplied with electric power.Examples for such loads 7 are incandescent lamps, inductive loads, e.g.,coils, motors, etc. FIG. 3B also shows the temperature differenceΔT=T1−T2 depending on the described voltage drop V_(DS). The arrowsalong the temperature difference curve ΔT indicate the progress in time.

In the very first moment after switching the power semiconductor chip 1of FIG. 1 from the OFF-state to the ON-state (see in FIG. 3B point oftime t0) due to the very low resistance of the load 7 most of the supplyvoltage V_(B) (in the example about 16 V) drops across the powersemiconductor switch 1 between the first load terminal 11 and the secondload terminal 12, i.e., the voltage drop V_(DS) is less than but almostequal to the supply voltage V_(B). Presumed that the power semiconductorswitch 1 was, prior to the point of time t0, in the OFF-state longenough to allow for a temperature equalization in the semiconductor chip1, the first temperature T1 and the second temperature T2 are equal,i.e., the temperature difference ΔT=T1−T2 is zero at t0.

At a later point of time t1, due to an increased resistance of the load7, the voltage drop V_(DS) is reduced to about 6 V, and the temperaturedifference ΔT=T1−T2 is about 45 K. In the same way, up to a point oftime t2 which is later than the point of time t1, the voltage dropV_(DS) is continuously reduced, whilst the temperature differenceΔT=T1−T2 increases up to about 80 K. In the period between t0 and t2, atany point of time the temperature difference ΔT=T1−T2 is less than thepredefined switching-OFF threshold temperature difference ΔT_(OFF).Therefore, in the period between t0 and t2 the voltage V1 provided bythe temperature difference evaluation unit 8 is less than the voltage V2provided at the output 93 of the first threshold providing unit 9, i.e.,the voltage difference V1−V2 is negative and the signal provided at theoutput 33 of the first comparator unit 3 causes the power semiconductorswitch 1, via the interconnected gate driving unit 5, to remain in theON-state.

However, at the point of time t2, when the voltage drop V_(DS) is about3 V, the temperature difference ΔT=T1−T2 is equal to the predefinedswitching-OFF threshold temperature difference ΔT_(OFF), i.e. thevoltages V1 and V2 applied to the respective inputs 31 and 32 of thefirst comparator unit 3 are equal so that the first comparator unit 3changes its output signal provided at the output 33 in order to causethe gate driving unit 5 to switch the power semiconductor switch 1 OFF.Hence, the voltage drop V_(DS) increases to about 16 V (see point oftime t3). Then, the lamp cools down and the temperature difference ΔTbegins to decrease until at a point of time t0′, the temperaturedifference ΔT is equal to a predefined switching-ON thresholdtemperature difference ΔT_(ON). A first cycle is completed, and, at t0′,the power semiconductor switch 1 is switched ON again, a second cyclestarts.

With an increasing resistance of the load 7 the voltage drop V_(DS)decreases, thereby passing a point of time t1′, until, at a point oftime t2′, the temperature difference ΔT=T1−T2 and the switching-OFFthreshold temperature difference ΔT_(OFF) are equal and the powersemiconductor switch 1 is switched OFF again. The voltage drop V_(DS)increases again to about 16 V (see point of time t3′), the lamp coolsdown and the temperature difference ΔT begins to decrease until—at apoint of time t0″—the temperature difference ΔT is equal to theswitching-ON threshold temperature difference ΔT_(ON). The second cycleis completed, and, at t0″, the power semiconductor switch 1 is switchedON again, a third cycle starts.

In this way, cycling continues until the temperature difference ΔTremains constantly lower than the switching-OFF threshold temperaturedifference ΔT_(OFF).

In the arrangement of FIG. 1, the predefined switching-ON thresholdtemperature difference ΔT_(ON) is represented by a voltage V2′, which isgenerated by a second threshold providing unit 9′. The voltage V1representing the temperature difference ΔT=T1−T2 and the voltage V2′ arefed to respective inputs 41 and 42 of a second comparator unit 4. Aslong as the voltage V1 provided by the temperature difference evaluationunit 8 is greater than the voltage V2′ provided at the output 93′ of thesecond threshold providing unit 9′, i.e., as long as the voltagedifference V1−V2′ is negative, an output signal provided at the output43 of the second comparator unit 4 causes the power semiconductor switch1, via the interconnected gate driving unit 5, to remain in theOFF-state.

However, at the point of time t0′ the temperature difference ΔT=T1−T2 isequal to the predefined switching-ON threshold temperature differenceΔT_(ON), i.e., the voltages V1 and V2′ applied to the respective inputs41 and 42 of the second comparator unit 4 are equal so that thecomparator unit 4 changes its output signal provided at the output 43 inorder to cause the gate driving unit 5 to switch the power semiconductorswitch 1 ON.

Due to the switching delay, in particular, of the second comparator unit4, of the gate driving unit 5 and of the power semiconductor switch 1,the power semiconductor switch 1 is effectively switched ON at a pointof time t5 which is later than the point of time t4, i.e., thetemperature difference ΔT=T1−T2 decreases in the period between t4 andt5. However, at t5 there the current I_(DS) through the powersemiconductor switch 1 and, accordingly, the temperature difference ΔTbegin to increase.

Then, at a point of time t6 the temperature difference ΔT=T1−T2 and thepredefined switching-OFF threshold temperature difference ΔT_(OFF) areequal again, i.e., the voltages V1 and V2 applied to the respectiveinputs 31 and 32 of the first comparator unit 3 are equal so that thefirst comparator unit 3 changes its output signal provided at the output33 in order to cause the gate driving unit 5 to switch the powersemiconductor switch 1 OFF and the cycle starts anew as described withreference to the period from t2 to t6.

In the previous example, the signals provided by the temperaturedifference evaluation unit 8, by the first threshold providing unit 9,by the second threshold providing unit 9′, by the first comparator unit3, by the second comparator unit 4, and by the gate driving unit 5 havebeen described as voltages. However, any other signals, e.g., currents,digital signals including signals exchanged by bus systems, areapplicable as well. Moreover, the signals do not necessarily need tohave the algebraic sign as described above. Any other sign, if any, isapplicable as well.

In FIG. 1, the first threshold providing unit 9 and the second thresholdproviding unit 9′ were described in a simplified manner only. FIGS. 2Aand 2B show possibilities how the first threshold providing unit 9and/or the second threshold providing unit 9′, respectively, may berealized. In FIG. 2A, the first threshold providing unit 9 comprises anoperational amplifier with an (inverting) first input 91, a second input92, and an output 93. The first input 91 is connected to the first loadterminal 11, the second input 92 to the second load terminal 12, so asto provide an output signal at the output 93 which may be proportionalto the voltage difference between the inputs 91 and 92, i.e., to thevoltage drop V_(DS). Depending on the requirements of the particularapplication, a gain factor or an attenuation factor, and/or an offsetvoltage may be implemented if necessary. In FIG. 2A, an increasingvoltage drop V_(DS) results in a decreasing output voltage V2.Generally, the characteristic of the operational amplifier may be linearor non-linear, but not constant. The respective circuitry of theoperational amplifier required to achieve the predefined output signalis not shown in FIG. 2A.

As shown in FIG. 2B, the output voltage V2′ may be provided by thesecond threshold providing unit 9′ in the same way as the output voltageV2 is provided by the first threshold providing unit 9. Thecharacteristic of the operational amplifier of the second thresholdproviding unit 9′ shown in FIG. 2B may also be linear or non-linear, butalso constant. The inputs 91′, 92′ and the output 93′ correspond withthe inputs 91, 92 and the output 93, respectively, shown in FIG. 2A. Thecurve progression of the predefined switching-OFF threshold temperaturedifference ΔT_(OFF)(V_(DS)) may be monotonic decreasing with V_(DS),i.e.,

$\begin{matrix}{\frac{\partial\left( {\Delta \; T_{OFF}} \right)}{\partial V_{{DS}\mspace{11mu}}} \leq 0} & (1)\end{matrix}$

Alternatively, the curve progression of the predefined switching-OFFthreshold temperature difference ΔT_(OFF)(V_(DS)) may be strictlymonotonic decreasing with V_(DS), i.e.,

$\begin{matrix}{\frac{\partial\left( {\Delta \; T_{OFF}} \right)}{\partial V_{DS}} < 0} & (2)\end{matrix}$

The curve progression of the predefined switching-ON thresholdtemperature difference ΔT_(ON)(V_(DS)) may be monotonic decreasing withV_(DS), i.e.,

$\begin{matrix}{\frac{\partial\left( {\Delta \; T_{ON}} \right)}{\partial V_{{DS}\;}} \leq 0} & (3)\end{matrix}$

Alternatively, the curve progression of the predefined switching-ONthreshold temperature difference ΔT_(ON)(V_(DS)) may be strictlymonotonic decreasing with V_(DS), i.e.,

$\begin{matrix}{\frac{\partial\left( {\Delta \; T_{ON}} \right)}{\partial V_{DS}} < 0} & (4)\end{matrix}$

Further, the predefined switching-ON threshold temperature differenceΔT_(ON) may be defined as constant.

Optionally, the predefined switching-OFF threshold temperaturedifference ΔT_(OFF)(V_(DS)) may be defined to be greater than thepredefined switching-ON threshold temperature difference ΔT_(ON)(V_(DS))at any voltage drop V_(DS).

In cases where the switching delay, in particular, of the firstcomparator unit 3, of the gate driving unit 5 and of the powersemiconductor switch 1 is large, it may also be applicable to define theswitching-OFF threshold temperature difference ΔT_(OFF)(V_(DS)) and thepredefined switching-ON threshold temperature difference ΔT_(ON)(V_(DS))to be equal for any voltage drop V_(DS). In these cases, only one of thefirst comparator unit 3 and the second comparator unit 4 is required.

FIG. 4 is a diagram showing the electrical current I_(DS) through thepower semiconductor switch 1 of FIG. 1, and the temperature differenceΔT=T1−T2 between the first temperature T1 and the second temperature T2,as a function of the time t, when switching ON the power semiconductorswitch, wherein the load 7 is an incandescent lamp. The incandescentlamp is intended to be switched on. However, within a turn-on periodΔt_(ON), the filament of the lamp is comparatively cold and thereforehas a comparatively low resistance which causes the power semiconductorswitch 1 to be alternately switched OFF and ON several times asdescribed with reference to FIG. 3B. After a while, if the resistance ofthe filament is high enough, the temperature difference ΔT decreases andthe power semiconductor switch 1 remains in the ON-state continuously.

FIG. 5 is a diagram showing the electrical current I_(DS) through thepower semiconductor switch 1 of FIG. 1, and the temperature differenceΔT=T1−T2 between the first temperature T1 and the second temperature T2,as a function of the time t, in the case of an electric short circuit.During a short circuit, the voltage drop V_(DS) will be almost identicalto the supply voltage V_(B) and the power semiconductor switch 1 isheated to high temperatures T1. Accordingly, the temperature differenceΔT=T1−T2 increases and the power semiconductor switch 1 is switched OFF.After cooling down, the power semiconductor switch 1 is switched ONagain. However, due to the short circuit the load 7 is bypassed and doesnot act as a protective resistor for the power semiconductor switch 1,i.e., alternately switching the power semiconductor switch 1 OFF and ONis continued.

FIG. 6 is top view of power semiconductor chip 61 comprising allcomponents shown in FIG. 1 except the load 7 and the power supply V_(B).The power semiconductor chip 61 includes the power semiconductor switch1 with the first load terminal 11 and the second terminal 13 on top.Additionally, a control circuitry 62 comprising the temperaturedifference evaluation unit 8, the first and second threshold providingunits 9 and 9′, respectively, and the first and second comparator units3 and 4, respectively, is arranged on the power semiconductor chip 61.The first temperature sensor 21 is arranged in the area of the powersemiconductor switch 1. The second temperature sensor 22 however isarranged distant from the power semiconductor switch 1 in the area ofthe control circuitry 62. The power semiconductor chip 61 and thecontrol circuitry 62 including the respective components are arranged incommon housing 60 which is indicated as a dashed line. The powersemiconductor chip 61 further comprises leads 63. The required electricconnections of the arrangement are suppressed in FIG. 6.

Although specific examples have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that avariety of alternate and/or equivalent implementations may besubstituted for the specific examples shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specific examplesdiscussed herein. Therefore, it is intended that this invention belimited only by the claims and the equivalents thereof.

Finally it should be noted that device features or method steps thathave been explained in terminal with one example may be combined withdevice features or method steps of other examples also in those cases inwhich such combinations have not explicitly been explained. Inparticular, features or method steps mentioned in a claim may becombined with features or method steps mentioned in any one or moreother claims within the same embodiment, as long as the respectivefeatures or method steps do not exclude each other.

1. A method for operating a power semiconductor circuit arrangement, themethod comprising: providing a power semiconductor chip comprising apower semiconductor switch with a first load terminal and with a secondload terminal; providing a first temperature sensor that is thermallycoupled to the power semiconductor switch; providing a secondtemperature sensor; and switching OFF the power semiconductor switch orkeeping the power semiconductor switch switched OFF if a temperaturedifference between a first temperature of the first temperature sensorand a second temperature of the second temperature sensor is greaterthan or equal to a switching-OFF threshold temperature difference whichdepends, following an inconstant first function, on a voltage drop overthe power semiconductor switch between the first load terminal and thesecond load terminal.
 2. The method of claim 1, further comprising:switching ON the power semiconductor switch or keeping the powersemiconductor switch switched ON if the temperature difference betweenthe first temperature and the second temperature is less than or equalto a switching-ON threshold temperature difference which depends,following a second function, on the voltage drop over the powersemiconductor switch between the first load terminal and the second loadterminal.
 3. The method of claim 2, wherein the second function isinconstant.
 4. The method of claim 3, wherein the switching-OFFthreshold temperature difference is greater than the switching-ONthreshold temperature difference at any voltage drop.
 5. The method ofclaim 2, wherein the second function is constant.
 6. The method of claim1, wherein the temperature difference between the first temperature andthe second temperature is represented by a first voltage, and whereinthe switching-OFF threshold temperature difference is represented by asecond voltage.
 7. The method of claim 6, wherein the first voltage andthe second voltage are fed to a comparator that keeps the powersemiconductor switch switched OFF if the first voltage is greater thanor equal to the second voltage.
 8. The method of claim 1, wherein thepower semiconductor chip, the first temperature sensor and the secondtemperature sensor are integrated in a common housing.
 9. The method ofclaim 8, wherein the first temperature sensor and the second temperaturesensor are integrated in the power semiconductor chip.
 10. A powersemiconductor circuit arrangement comprising: a power semiconductor chipcomprising a power semiconductor switch with a first load terminal andwith a second load terminal; a first temperature sensor that isthermally coupled to the power semiconductor switch; a secondtemperature sensor; and an electrical circuit designed to switch OFF thepower semiconductor switch or to keep the power semiconductor switchswitched OFF if a temperature difference between a first temperature ofthe first temperature sensor and a second temperature of the secondtemperature sensor is greater than or equal to a switching-OFF thresholdtemperature difference which depends, following an inconstant firstfunction, on a voltage drop over the power semiconductor switch betweenthe first load terminal and the second load terminal.
 11. The powersemiconductor circuit arrangement of claim 10, wherein the electricalcircuit is designed to switch ON the power semiconductor switch or tokeep the power semiconductor switch switched ON if the temperaturedifference between the first temperature and the second temperature isless than or equal to a switching-ON threshold temperature differencewhich depends, following a second function, on the voltage drop over thepower semiconductor switch between the first load terminal and thesecond load terminal.
 12. The power semiconductor circuit arrangement ofclaim 11, wherein the second function is inconstant.
 13. The powersemiconductor circuit arrangement of claim 12, wherein the switching-OFFthreshold temperature difference is greater than the switching-ONthreshold temperature difference at any voltage drop.
 14. The powersemiconductor circuit arrangement of claim 11, wherein the secondfunction is constant.
 15. The power semiconductor circuit arrangement ofclaim 10, wherein the temperature difference between the firsttemperature and the second temperature is represented by a firstvoltage, and wherein an actual switching-OFF threshold temperaturedifference is represented by a second voltage.
 16. The powersemiconductor circuit arrangement of claim 15, comprising a comparatorwith a first input and with a second input, wherein the first voltage issupplied to the first input, the second voltage is supplied to thesecond input, and wherein the comparator is designed to switch OFF thepower semiconductor switch or to keep the power semiconductor switchswitched OFF, if the first voltage is greater than or equal to thesecond voltage.
 17. The power semiconductor circuit arrangement of claim10, wherein the power semiconductor chip, the first temperature sensorand the second temperature sensor are integrated in a common housing.18. The power semiconductor circuit arrangement of claim 17, wherein thefirst temperature sensor and the second temperature sensor areintegrated in the power semiconductor chip.
 19. The power semiconductorcircuit arrangement of claim 10, comprising an incandescent lamp that iselectrically connected to the first load terminal or to the second loadterminal.
 20. The power semiconductor circuit arrangement of claim 19,wherein the incandescent lamp is a lamp of a vehicle.
 21. The powersemiconductor circuit arrangement of claim 10, wherein the powersemiconductor switch is a DMOS transistor.
 22. A power semiconductorcircuit arrangement comprising: a power semiconductor switch with afirst load terminal, a second load terminal and a control input; a firsttemperature sensor thermally coupled to the power semiconductor switch;a second temperature sensor; a temperature difference evaluation unitwhich is designed to provide a first voltage at a first output, thefirst voltage representing a temperature difference between atemperature of the first temperature sensor and a temperature of thesecond temperature sensor; a threshold providing unit to provide asecond voltage at a second output, the second voltage representing aswitching-OFF threshold temperature difference from an inconstant firstfunction at a voltage difference measured between the first loadterminal and the second load terminal, wherein the first function is aswitching-OFF threshold temperature difference depending on a voltagedrop; a comparator unit comprising a first comparator input, a secondcomparator input, and a comparator output, wherein the first output iselectrically connected to the first comparator input, wherein the secondoutput is electrically connected to the second comparator input, andwherein the comparator output is electrically connected to the controlinput of the power semiconductor switch; and wherein the comparator unitis designed to provide a signal causing the power semiconductor switchto remain or to be switched in an OFF-state, if the voltage differencebetween the first voltage and the second voltage implies that atemperature difference determined by the temperature differenceevaluation unit is greater than or equal to a switching-OFF thresholdtemperature difference determined by the threshold providing unit. 23.The power semiconductor circuit arrangement of claim 22, furthercomprising a gate driving unit with an input and with an output, whereinthe comparator output is electrically connected to the input of the gatedriving unit, and wherein the output of the gate driving unit iselectrically connected to the control input of the power semiconductorswitch.
 24. The power semiconductor circuit arrangement of claim 22,wherein the threshold providing unit is designed as an analog circuit.25. The power semiconductor circuit arrangement of claim 22, wherein apredefined switching-OFF threshold temperature difference is monotonicdecreasing with the voltage difference measured between the first loadterminal and the second load terminal.
 26. The power semiconductorcircuit arrangement of claim 22, further comprising: a further thresholdproviding unit to provide a third voltage at a third output, the thirdvoltage representing a switching-ON threshold temperature differencefrom a second function at a voltage difference measured between thefirst load terminal and the second load terminal, wherein the secondfunction is a switching-ON threshold temperature difference depending ona voltage drop; a further comparator unit comprising a third comparatorinput, a fourth comparator input, and a further comparator output,wherein the first output is electrically connected to the thirdcomparator input, wherein the third output is electrically connected tothe fourth comparator input, and wherein the comparator output iselectrically connected to a further control input of the powersemiconductor switch; and wherein the further comparator unit isdesigned to provide a signal causing the power semiconductor switch toremain or to be switched in an ON-state, if the voltage differencebetween the first voltage and the second voltage implies that atemperature difference determined by the temperature differenceevaluation unit is less than or equal to a switching-ON thresholdtemperature difference determined by the further threshold providingunit.